As a dynode unit of an electron multiplier, an arrangement, wherein a plurality of dynodes are positioned in a layered state in multiple stages, is generally known (see, for example, Patent Document 1). In an electron multiplier equipped with this type of dynode, a plurality of stem pins, for supplying control voltages to the respective dynodes, are fixed in a penetrating manner in a stem plate that makes up a vacuum container of the electron multiplier, and by the tip portions of the respective stem pins being fixed to peripheral portions of the respective dynodes, the plurality of dynodes are supported in multiple stages in a mutually parallel manner (see, for example, Patent Document 2).
Here, with the electron multiplier described in Patent Document 2, in order to keep uniform the mutual intervals of the plurality of dynodes that are supported in multiple stages, microscopic insulation balls are interposed between opposing surfaces of the respective dynodes. The insulating balls are fitted into tapered-hole-like recesses, which are formed on the opposing surfaces of the dynodes, and are thereby prevented from falling off.    Patent Document 1: Japanese Published Unexamined Patent Application No. 2000-3693 (FIG. 1)    Patent Document 2: Japanese Published Unexamined Patent Application No. H8-7825 (FIG. 1)